Perception and attention form the foundations of cognitive processing within the human nervous system. The study of event related potentials (ERPs) in the past 2 decades has revealed a great deal concerning the timing and functional properties of brain events related to detection, identification, and discrimination. However, the anatomical loci of the generators of these ERPs remains a mystery. We propose to utilize newly developed magnetoencephalographic (MEG) techniques to map the magnetic fields associated with components of ERPs evoked by perceptual processing as a means of specifying the three dimensional locus of these current generators. Two types of experiments, one involving detection and identification, the other discrimination, are proposed for each of three sensory modalities, audition, vision, and somatosensation. The experiments proposed should reveal the intracraneal locus ana modality specificity of the current sources associated with several ERP components, including N100, P300, the late positive wave, and the slow negative shift. By providing this much needed localizing information, previously obtained data concerning ERP components and perceptual processing may be given an anatomical and functional interpretation. Such results will be of major importance of theories of perception and attention in the human nervous system. The results of this research will be of relevance to a number of scientific disciplines, including human neurophysiology, sensory physiology, neurology, functional neuroanatomy, and cognitive science.